Subsea Control Modules, also called SCM's, are commonly used to provide well control functions during the production phase of subsea oil and gas production. Typical well control functions and monitoring provided by the subsea control module include the following: 1) actuation of fail-safe return production tree actuators and downhole safety valves; 2) actuation of flow control choke valves, shut-off valves, etc.; 3) actuation of manifold diverter valves, shut-off valves, etc.; 4) actuation of chemical injection valves; 5) actuation and monitoring of Surface Controlled Reservoir Analysis and Monitoring Systems (SCRAMS) sliding sleeves, choke valves; 6) monitoring of downhole pressure, temperature and flow rates; and 7) monitoring of sand probes, production tree and manifold pressures, temperatures, and choke positions.
The close proximity of the typical subsea control module to the subsea production tree, coupled with its electro-hydraulic design allows for quick response times of tree valve actuations. The typical subsea control module receives electrical power, communication signals and hydraulic power supplies from surface control equipment. The subsea control module and production tree are generally located in a remote location relative to the surface control equipment. Redundant supplies of communication signals, electrical, and hydraulic power are transmitted through umbilical hoses and cables of various length, linking surface equipment to subsea equipment. Electronics equipment located inside the subsea control module conditions electrical power, processes communications signals, transmits status and distributes power to devices such as solenoid piloting valves, pressure transducers and temperature transducers.
Low flow rate solenoid piloting valves are typically used to pilot high flow rate control valves. These control valves transmit hydraulic power to end devices such as subsea production tree valve actuators, choke valves and downhole safety valves. The status condition of control valves and their end devices are read by pressure transducers located on the output circuit of the control valves. Auxiliary equipment inside the typical subsea control module consists of hydraulic accumulators for hydraulic power storage, hydraulic filters for the reduction of fluid particulates, electronics vessels, and a pressure/temperature compensation system.
Subsea drilling control systems include a large blowout preventer (BOP) systems and a lower marine riser package (LMRP) that allows quick disconnection from the blowout preventer in the event of an emergency. Typically, the BOP has two redundant subsea control modules having electrical and hydraulic components for controlling the BOP and LMRP. Each subsea control module is fairly large and complex as they control many different functions, such as the various rams and closure elements, connectors and the like of the BOP. If a problem is detected, one of the subsea control modules may be retrieved, usually on a lift line, while the other maintains operation of the BOP.